Ischemic disorders are disorders caused by significant stagnation of blood supply to organs and tissues due to arteriosclerosis, organ transplantation, cardiovascular abnormality, arrest of bleeding during surgery, etc. It is known that exposure of organs and tissues in ischemic conditions to reoxygenation by reflow of blood (reperfusion) causes inflammatory reactions which induce ischemia-reperfusion injury. Particularly, myocardial tissue depends mainly on aerobic metabolisms, and its demanded oxygen is supplied from coronary arteries. The myocardial tissue, as compared with other tissues, requires higher oxygen consumption, and the oxygen uptake rate in the heart from coronary arterial blood, even at rest, is considered to be almost about 75% of the maximum. Accordingly, increase of myocardial oxygen demand in coronary circulation is hardly regulated by oxygen uptake rate and is regulated mainly by coronary blood flow.
As described above, cardiac muscle is vulnerable to ischemia, and that occlusion of coronary arteries by angiospasm, thrombus, arteriosclerosis etc. damages myocardial cells. As a result, the cardiac muscle undergoes an angina attack due to temporary ischemic conditions, and causes myocardial infarct due to long standing obstruction of blood flow. The heart disease resulting from myocardial ischemia is called an ischemic heart disease.
Therapy of ischemic heart disease has been carried out by drug treatments with therapeutic drugs which reduce cardiac load such as β-blockers and long-acting nitrate drugs and therapeutic drugs which have a coronary dilation activity such as calcium antagonists and nitrate drugs. Further, in therapy of e.g. acute myocardial infarct having a high mortality rate of around 30%, it is considered effective to administer thrombolytic agents, and to give reperfusion treatment such as percutaneous transluminal coronary angioplasty (PTCA or POBA), rotarblator, directional coronary atherectomy (DCA), coronary intervention with a stent and the like (see, for example, Non-Patent Documents 1, 2 and 3). These therapies ameliorate ischemic conditions, however there has been a problem that temporary ischemic conditions cause cell dysfunctions etc., and the functions of the heart are not completely recovered even if the ischemic conditions have been ameliorated. The heart diseases still remain major causes of death in the world, and there has been demand for more effective therapeutic drugs.
It is known that although large coronary artery constriction is relieved by reperfusion therapy such as coronary intervention, subsequently occurred severe inflammatory reactions, apoptosis, etc., due to recanalization, damage cardiac muscle (reperfusion damage) or subsequently manifested lethal arrhythmia causes sudden death, and thus the death rate in hospitals is as high as about 10% even after treatment. Even in the case reperfusion therapy has been successful if extensive myocardial damage remains, severe heart malfunction may readily cause cardiac failure and patients are accompanied by the risk of sudden death from lethal arrhythmia. It is thus considered extremely important to prevent, by initial therapy at the acute stage, reperfusion injury and spread of an injured area. The cause of reperfusion injury has been considered to lie in activation of inflammatory cells such as neutrophils and in transient enhanced expression of cytokines and adhesion molecules by vascular endothelial cells, but a true target for preventing or treating the reperfusion injury has not been found.
Nitric oxide synthase (NOS) is an enzyme that uses L-arginine as a substrate to produce nitric oxide (NO), and known as neuronal NOS (n-NOS), inducible NOS (i-NOS), and endothelial NOS (eNOS). NO produced by eNOS is distributed mainly in vascular endothelial cells and activates soluble guanylate cyclase in vascular smooth muscle cells to promote increases in cGMP, thereby relaxing the blood vessels. It has been reported that, in ischemic disorders and ischemia-reperfusion injury, NO derived from eNOS has protective effects on blood vascular systems, such as a platelet aggregation inhibiting effect, an effect of inhibiting the adhesion and infiltration of leukocytes into vascular endothelium (inhibitory action on expression of adhesion molecules), an NF-κB activity-inhibiting effect, an inhibitory effect on growth of vascular smooth muscle cells, a superoxide scavenger effect, etc. It is known that, after reperfusion, vascular endothelial cells are damaged and the eNOS-mediated production of NO is reduced. Supply of a suitable amount of NO during an ischemia (reperfusion) period may permit maintenance of blood flow in a border zone between local ischemia and normal tissue and may suppress cell dysfunctions by regulating infiltration with inflammatory cells, and thus has drawn the interest as a therapeutic method for ischemia (reperfusion).
Midkine (referred to hereinafter as “MK”) is a cell growth factor or a cell differentiation factor found as a gene product expressed transiently in a process of differentiation induction of embryonal cancer cells by retinoic acid, and is a basic amino acid- and cysteine-enriched polypeptide with a molecular weight of 13 kDa (see, for example, Non-Patent Documents 4 and 5). The amino acid sequence of MK has 50% homology with pleiotrophin (PTN), and these proteins are considered as heparin-binding family proteins. The inventors previously found that MK is effective in prevention and treatment of the above-mentioned ischemic cell dysfunction and/or myocardial cell dysfunction after ischemia-reperfusion (see Patent Document 1), and also that the preventive and therapeutic effect of MK on the ischemic cell dysfunction and/or myocardial cell dysfunction after ischemia-reperfusion is based partly on its apoptosis-suppressing action (see Patent Documents 2, 3 and 4 and Non-Patent Document 6). PTN that is a family protein of MK has been reported to have an angiogenic activity, and MK, similar to the family protein PTN, has been considered to have an angiogenic activity (see Patent Document 5).
The inventors have previously administered MK to a model mouse via an osmotic pump in verifying the therapeutic effect of MK on myocardial cell dysfunction after ischemia-reperfusion based on MK' s apoptosis-suppressing action (see Patent Document 4). The administration via an osmotic pump is easily utilized in the in vivo evaluation of the effectiveness of the drug, but cannot be used in actual human treatment, and therefore, there has been necessity for establishment of the optimum method of administration to be applied to human treatment or prevention.
In the treatment of ischemic heart disease by a cell growth factor, it has been reported that because the drug, hardly reaches cardiac muscle by intravascular administration such as intracoronary administration and intravenous administration, and can thus not achieve a sufficient effect (see Non-Patent Documents 7 and 8). In order to increase the efficiency of incorporation of the drug into cardiac muscle, various administration ways such as direct injection into cardiac muscle, high-pressure retrograde administration to coronary veins (see Non-Patent Document 9) and rapid injection into coronary arteries (Non-Patent Documents 10 and 11) have been devised and verified. However, these administration ways are complicated and hardly practically usable, and their effect is not sufficient. Thus, an efficient administration method has not been found, and an easy and therapeutically effective administration method is needed.    Patent Document 1: International Publication No. 1999/16463    Patent Document 2: International Publication No. 2000/02578    Patent Document 3: JP-A 2005-68122    Patent Document 4: International Publication No. 2006/062087    Patent Document 5: International Publication No. 1999/053943    Non-Patent Document 1: The New England Journal of Medicine (2007); 356: 47-54    Non-Patent Document 2: J. Am. Coll Cardio. (2000); 36: 2056-63    Non-Patent Document 3: Am. Heart J. (2004); 148: S29-33    Non-Patent Document 4: Kadomatsu, K. et al.: (1988) Biochem. Biophys. Res. Commun., 151: p. 1312-1318    Non-Patent Document 5: Tomokura, M. et al.: (1999) J. Biol. Chem. 265: p. 10765-10770    Non-Patent Document 6: Mitsuru Horiba, et al.: (2006) Circulation, 114: p. 1713-1720    Non-Patent Document 7: M. Roger J. Laham, et al.: (2003) Catheterization and Cardiovascular Interventions, 58: p. 375-381    Non-Patent Document 8: Timothy D. Henry, et al.: (2003) Circulation, 107: p. 1359-1365)    Non-Patent Document 9: William F. Fearon, et al.: (2004) Catheterization and Cardiovascular Interventions, 61: p. 422-428    Non-Patent Document 10: Michael Simons, et al.: (2002) Circulation, 105: p. 788-793    Non-Patent Document 11: John J. Lopez, et al.: (1998) Cardiovascular Research, 40: p. 272-281